Fix typo of 7-point gauss rule (#14808)

QUADPACK: dqk15w.f: line #103, wrong weights of the 7-point gauss rule
The weights of wg should be the same as "dqk15.f":
#103: "0.3818300505051889d+00", should be changed to "0.3818300505051189d+00".
This is a historical typo that commonly exists in every code that embeds netlib-quadpack, which does not necessarily produce an actual numerical error in the calculation of the error of the quadrature using the Gauss-Kronrod rule.

Reviewed/discussed in #14807.

An upstream fix at netlib/quadpack made on 05 Oct 2021, see #14807 (comment)

scipy/integrate/quadpack/dqk15w.f

@@ -100,7 +100,7 @@ subroutine dqk15w(f,w,p1,p2,p3,p4,kp,a,b,result,abserr,
 c
       data wg(1),wg(2),wg(3),wg(4)/
      *     0.1294849661688697d+00,    0.2797053914892767d+00,
-     *     0.3818300505051889d+00,    0.4179591836734694d+00/
+     *     0.3818300505051189d+00,    0.4179591836734694d+00/
 c
 c
 c           list of major variables